As a motion guide device of this type, there has been known one disclosed in Patent Literature 1. The motion guide device includes a raceway rail including rolling surfaces for rolling elements formed along a longitudinal direction, a moving block assembled to the raceway rail through intermediation of a large number of rolling elements which roll on the rolling surface and including an endless circulation path for the rolling elements, and a plurality of separators to be moved together with the rolling elements in the endless circulation path of the moving block. Along with circulation of the rolling elements in the endless circulation path, the moving block and the raceway rail can reciprocate relative to each other.
The moving block includes a block body including load rolling element paths in which the rolling elements roll under load between the raceway rail and the moving block, and rolling element return paths provided parallel to the load rolling element paths, and a pair of end plates each including a pair of direction turning paths each connecting the load rolling element path and the rolling element return path to each other so as to form the endless circulation path, the pair of end plates being fixed to the block body. Further, the separators are arranged between the rolling elements in a manner that an axial line of each of the separators and a straight line connecting center points of adjacent the ones of the rolling elements to each other correspond to each other. Further, spherical seats in conformity with an outer peripheral shape of the rolling elements are formed on contact surfaces of each of the separators with respect to the rolling elements.
In the motion guide device of Patent Literature 1, which is structured as described above, when the rolling elements enter the direction turning path, the rolling elements roll in a circular-arc form along an outer peripheral side guide curved surface of the direction turning path. Meanwhile, the separators are arranged so that the axial line of each of the separators and the straight line connecting the center points of adjacent ones of the rolling elements to each other correspond to each other. Thus, at the same time when the rolling elements pass through a start position of the outer peripheral side guide curved surface of the direction turning path and start to roll along the outer peripheral side guide curved surface toward a direction of being spaced apart from the rolling surface of the raceway rail, the separators held in contact with the rolling elements through intermediation of the spherical seats gradually come closer to an inner peripheral side guide curved surface of the direction turning path with respect to the rolling elements. In order to prevent the separators and the inner peripheral side guide curved surface in the direction turning path from interfering with each other due to displacement of a track of the separators, in the motion guide device disclosed in Patent Literature 1, the inner peripheral side guide curved surface is formed into a compound curved surface including a plurality of curved surfaces having different curvatures.